This invention relates to a metal pipe coupling, and to be more precise, to a device for coupling lengths of metal pipe, too hard or too thin for cutting a screw, by inserting a screwed socket in one end of the pipe, expanding that part of the pipe, and joining it airtight with another coupling.
In prior art, according to the most widely adopted method of coupling lengths of metal pipe, a screw is cut in the end of a pipe and is screwed up with another pipe in the end of which also a corresponding screw is cut. Otherwise, in case the inside diameter of the pipe is large enough, or in case the pipe is for use under high pressure for special purposes, coupling with the use of flanges or the like is adopted.
The most common joint materials for coupling metal pipes are nipples, angles, tees, crosses, unions, or reducers, and in all cases of joint pipes a screw meeting the one in the joining material has to be cut in the end of the pipe which is to be coupled with another.
But in case a pipe is of metal extremely hard or too thin coupling by ordinary, conventional methods proves very difficult.
It is practically impossible to cut a screw with the use of die stocks or the like in case the pipe is of too hard metal, and even if it is any possible the screw cutting will cost too much time and money, resulting in lower productivity, lower yield as a matter of course. In case the metal of the pipe is very thin, the screws, if cut at all despite the practical impossibility, will leave the thickness of the metal at the part where a screw is cut too thin for it to bear a slightest pressure.